Stephen Colbert will host campaign fundraiser for his sister

Colbert joked about his sister's candidacy on the show shortly after she announced — though he'd promised to stay neutral.

"As a broadcast journalist, I'm obligated to maintain pure objectivity," he said on the show. "It doesn't matter that my sister is intelligent, hard-working, compassionate and dedicated to the people of South Carolina. I will not be mentioning any of that on my show."